Meristems 



63 



Fig. 4-9. At left, shoot apex of Abies pectinata, semidiagrammatic. At right, diagram 

 of confocal parabolas as postulated by Sachs from such an apex as that of Abies. 

 ( From Sachs. ) 



Even though layering may not be of primary significance, the general 

 pattern formed by the planes of cell division in the meristem is of in- 

 terest. Reinke (1880) and Sachs (1878) many years ago called attention 

 to the fact that the divisions approximately at right angles to the surface 

 of the meristem and axis and those parallel to it tend, if extended, to 

 form two sets of essentially parabolic curves with a common focus 

 just below the apex of the meristem ( Fig. 4-9 ) . This somewhat diagram- 

 matic interpretation of the situation has largely been neglected by 

 recent writers. Such a pattern can be found both in shoots and roots, 

 however, though it is often inconspicuous in small meristems. Foster 

 ( 1943 ) called attention to the observations of these early workers in his 

 study of the broad apices of certain cycads; and Schuepp, both in his 

 volume on meristems ( 1926 ) and in a later paper ( 1952 ) , has emphasized 

 it. The pattern made by these two series of curves is modified as they 



V ^2 



Fig. 4-10. Diagram of longitudinal section of broad apical shoot meristem of Micro- 

 cycas. 1, initiation zone; 2, central mother-cell zone; 3, peripheral zone; 4, zone of rib 

 meristem. Arrows represent lines of convergence of cells. (From Foster.) 



